The Collaborative International Dictionary of English v.0.48:

Pleurotoma \Pleu*rot"o*ma\, n.; pl. L. Pleurotom[ae], E.
   Pleurotomas. [NL., fr. Gr. ? the side + tomh` a cut.]
   (Zool.)
   Any marine gastropod belonging to Pleurotoma, and ether
   allied genera of the family Pleurotmid[ae]. The species are
   very numerous, especially in tropical seas. The outer lip has
   usually a posterior notch or slit.
   [1913 Webster]